b. y =25 x²– 3x + 15
c. y =34− x²+ 7x − 18
Kunci jawaban Matematika kelas 9 halaman 102
a. y = -6x²+ 24x – 19
a = -6 b = 24 c = -19
Maka:
-D/4a = -(b2 – 4ac) / 4c
-(242 – 4 (-6) (-19) / 4(-6)
= -(576 – 456)/-24 -(120)/-24
= 5
b. y = 2/5x2 – 3x + 15
a = 2/5 b = -3 c = 15
Maka:
-D/4a = -(b2 – 4ac) / 4c
-(-32 – 4(2/5) 15) / 4. 2/5
-(9-24)/8/5
15/ 8/5
= 15.5/8
= 75/8
c. y = -3/4x2 + 7x – 18
a = -3/4 b = 7 c = -18
Maka:
-D/4a = -(b2 – 4ac) / 4c
-(72 – 4(-3/4) (-18)) / 4 (-3/4)
=-(49-54) / -3
5/-3